A heavy-duty industrial-grade machine for boring a large plate workpiece, such as a sheet of glass, normally has upper and lower clamp elements one of which, normally the upper one, is vertically displaceable toward and away from the other, and upper and lower drill heads both vertically displaceable toward and away from each other. The workpiece is gripped between the clamp elements, and then the drill heads are moved toward each other to bore through the workpiece coaxially from opposite sides. Normally each such drill head has a spindle having at its business end a chuck holding an appropriate drilling tool, in the case of glass a diamond-grit hole saw.
These drill heads are normally mounted, in standard machine-tool fashion, on slides carried in T-slots of the frame or support of the boring machine. Although it is known, as for example from German Pat. No. 559,046, to mount half of the slide on a pivotal arm, nonetheless the vertical displacement of the tools into engagement with the workpiece is effected with a sliding action of the tool head on the end of the pivotal arm.
The problem with such a system is that the support structure for the tools is quite bulky. This bulkiness precludes ganging the machines for simultaneously performing a plurality of closely spaced bores in a workpiece. In addition when the machine is used with a glass workpiece the slide, which is relatively close to the working area, becomes fouled with glass dust and wears at a great rate.
The clamp elements are similarly slidable. Hence they normally have the same disadvantages.